1. Field of the Invention
The present invention relates to an inside measuring instrument.
2. Description of Related Art
There has been known a bore gauge as an inside measuring instrument which measures an inner diameter of a hole or an inner width dimension of a groove.
The bore gauge measures a displacement of a gauge head by converting the displacement into a displacement of a rod in a direction perpendicular to the gauge head.
As a bore gauge, there has been known a thin-bottom type bore gauge which is suitable for measuring a diameter near a bottom of a shallow hole or a bottomed hole (blind hole) (JP S62-44327 Y).
A thin-bottom type bore gauge will be briefly described.
FIG. 1 is an external view of a bore gauge 100.
FIG. 2 is an enlarged view of a head part 200.
Here, the head part 200 of the bore gauge 100 will be mainly described as a background of the present invention.
FIG. 3 is a cross-sectional view of the head part 200.
FIG. 4 is an exploded perspective view of the head part 200.
The head part 200 of the bore gauge 100 includes a head main body part 300, a lower rod 210, a gauge head 400, an anvil 240, and a guide member 230.
An outer diameter screw part 310 is formed at the upper end of the head main body part 300. The outer diameter screw part 310 is screwed and fixed in one end of a cylindrical body 110. A spindle (not illustrated) is inserted in the cylindrical body 110. The spindle is movably installed in an axial direction. A clamp holder 111 is mounted at the other end of the cylindrical body 110, and the clamp holder 111 holds a stem (not illustrated) of a dial gauge (not illustrated). The dial gauge (not illustrated) detects a moving amount of the spindle (not illustrated).
In the head main body part 300, a first hole 321 is bored along the axial line of the outer diameter screw part 310.
The lower rod 210 is inserted in the first hole 321, and the lower rod 210 and the spindle (not illustrated) are coaxial and movable along the coaxial line. Then, an upper end 211 of the lower rod 210 is in point-contact with a lower end of the spindle (not illustrated), and the lower rod 210 and the spindle (not illustrated) move together.
Note that, a first compression coil spring (not illustrated) is interposed between the lower rod 210 or the spindle (not illustrated) and the cylindrical body 110, and the lower rod 210 or the spindle (not illustrated) is biased downward (to the lower end side of the cylindrical body 110).
A bottom face 302 of the head main body part 300 is machined so as to be flat. Furthermore, a second hole 322, which communicates with the first hole 321 and is orthogonal to the first hole 321, is bored inside the head main body part 300 at the bottom face 302 side. The gauge head 400 is inserted in the second hole 322 and freely moves forward and backward. The forward/backward direction of the gauge head 400 is orthogonal to the moving direction of the spindle (not illustrated) and the lower rod 210.
A right triangular cam 330 is rotatably supported about an axis at a crossing point of the first hole 321 and the second hole 322. The base end of the gauge head 400 is in contact with one cam face of the cam 330, and the lower end of the lower rod 210 is in contact with the other cam face orthogonal to the one cam face. The cam 330 converts a forward/backward moving amount of the gauge head 400 in the right-angle direction and transfers the converted amount to the lower rod 210.
A long groove 420 having a predetermined length along the axial line is provided on the outside face of the gauge head 400, and a tip end of a lock plate 340 is engaged in the long groove 420. The lock plate 340 is pressed in from the bottom face 302 of the head main body part 300.
With the lock plate 340 and the long groove 420, a stopper, which is the forward movement limit and the backward movement limit of the gauge head 400, is formed.
The lower rod 210 or the spindle (not illustrated) is biased downward by the first compression coil spring (not illustrated), and the gauge head 400 is continuously biased in a protruding direction from the head main body part 300.
The anvil 240 is screwed in the head main body part 300 at the opposite side to the gauge head 400.
The guide member 230 is provided slidably in the forward/backward direction of the gauge head 400 at the right side of the head main body part 300 in the drawings. The head main body part 300 has a groove 304 in the center of the end face at the gauge head 400 side and a substantially U-shape viewed from a side. The opening of the groove 304 is parallel. The guide member 230 has a first groove 231 and a substantially U-shape in a plan view. The opening of the first groove 231 is perpendicular. Furthermore, the guide member 230 has a second groove 232 at the lower part of the guide member 230. The second groove 232 is orthogonal to the first groove 231 and has an opening in the lower face.
The guide member 230 is engaged with the groove 304 of the head main body part 300 from the front side (one side) of the head main body part 300. At this time, the first groove 231 and the second groove 232 of the guide member 230 are fitted on the side face of the head main body part 300.
Thus, the guide member 230 is guided to the side face of the head main body part 300 and freely moves forward and backward.
A second compression coil spring 233 is interposed between the guide member 230 and the head main body part 300.
With the function of the second compression coil spring 233, the guide member 230 is continuously biased in a protruding direction from the head main body part 300.
A screw 306 is screwed in the head main body part 300 from the front side (one side). The head of the screw 306 is caught by the front end of the guide member 230, and serves as a stopper for the guide member 230.
While the guide member 230 is being engaged with the head main body part 300, the guide member 230 has a substantially gate shape symmetrical with respect to the center axis of the gauge head 400 so as to cover the gauge head 400 from above. Furthermore, a semicircular protrusion 236, which is a protrusion having a substantially semicircular shape, is integrally formed at the right side of the guide member 230 in the drawings. The center of the semicircular protrusion 236 coincides with the axial line of the gauge head 400, and the periphery of the semicircular protrusion 236 is smoothly round-chamfered. When the semicircular protrusion 236 is being firmly brought into contact with a measurement target surface, such as a hole, the gauge head 400 is to be perpendicularly brought into contact with the measurement target surface. The forward/backward moving amount of the gauge head 400 at this time is transferred to the dial gauge (not illustrated) through the lower rod 210 and the spindle (not illustrated), and a measurement value of an inner diameter is obtained from a value displayed on the dial gauge (not illustrated) accordingly.
In the above described configuration, most of the components of the head part 200 are provided above the axial line of the gauge head 400.
Thus, the size between the axial line of the gauge head 400 and the bottom face 302 of the head main body part 300 is shortened accordingly, and the bore gauge 100 is suitable for measuring a diameter near a bottom of a shallow hole or a blind hole.
Especially, biasing means, such as a spring, is not directly provided at the gauge head 400, and the force of the first compression coil spring (not illustrated) is biased by being indirectly transferred to the gauge head 400 through the lower rod 210 or the spindle (not illustrated). From this point, the size from the center axis of the gauge head 400 to the bottom face 302 is to be shortened.